This disclosure relates to a mechanical noise suppression apparatus, a mechanical noise suppression method, a program and an imaging apparatus, and more particularly to a mechanical sound suppression apparatus and so forth for reducing mechanical noise such as motor noise upon optical zooming during video shooting in an imaging apparatus which includes a video shooting function with sound.
In recent years, as an imaging apparatus of a digital camera and so forth, an imaging apparatus has been proposed which includes a video shooting function with sound in addition to a camera function. An imaging apparatus of the type described has a problem in that mechanical noise such as motor noise upon optical zooming during video shooting is mixed into peripheral sound collected by a microphone, resulting in degradation of the recorded sound.
As a technique for removing noise mixed in a sound signal, a spectral subtraction method is known and disclosed, for example, in S. F. Boll, “Suppression of acoustic noise in speech using spectral subtraction,” IEEE Trans. Acoustics, Speech, and Signal Process, Vol. 27, No. 2, pp. 113-120, 1979 (hereinafter referred to as Non-Patent Document 1). According to the spectral subtraction method, a spectrum within a no-sound period is estimated as a noise spectrum, and a signal obtained by multiplying the noise spectrum by a predetermined coefficient, that is, by a subtract coefficient, is subtracted from an input sound spectrum to remove a noise component.
With the method of estimating a spectrum within a no-sound period as a noise spectrum, mechanical noise generated independently of peripheral sound cannot be removed as noise as in such an imaging apparatus having a video shooting function with sound as described above. Therefore, it is proposed in Japanese Patent Laid-Open No. 2006-279185 (hereinafter referred to as Patent Document 1) to retain a frequency spectrum of mechanical noise upon optical zooming during video shooting in advance and subtract, upon zooming operation, the frequency spectrum of the mechanical noise from a spectrum of an input signal to reduce the mechanical noise.
FIG. 37 shows a configuration of a sound recording apparatus having a noise removing function disclosed in Patent Document 1. Referring to FIG. 37, a motor 21 moves a lens optical system such as a zoom lens in a direction of an optical axis. A motor driving section 21a is a driving mechanism for driving the motor 21 to rotate. A control section 32 receives an operation signal of a zoom key or the like included in a key inputting section 36 and outputs a motor driving controlling signal to the motor driving section 21a. Further, the control section 32 controls a spectrum changeover section 56 based on a driving timing of the motor 21 during video shooting with sound.
A sound inputting section 51 amplifies a sound signal Sa inputted thereto through a microphone not shown by a predetermined gain and supplies the amplified sound signal Sa to a framing section 52. In this instance, for example, if a zooming operation is carried out during video shooting with sound, then motor noise, that is, zooming noise, which is generated upon the zooming operation, is inputted to the framing section 52 together with the sound signal Sa through the sound inputting section 51. The framing section 52 divides the sound signal Sa inputted thereto from the sound inputting section 51 in a unit of a frame for a predetermined period of time. A Fourier transform section 53 Fourier transforms the sound signal Sa divided in a unit of a frame by the framing section 52 into a input sound spectrum Sb which indicates power for individual frequencies.
In a motor noise spectrum storage section 54, a motor noise spectrum Sc obtained by spectralizing motor noise which is an object of noise removal is stored as a noise spectrum. A subtract section 55 carries out a process of removing noise components based on the input sound spectrum Sb obtained by the Fourier transform section 53 and the motor noise spectrum Sc stored in the motor noise spectrum storage section 54. In particular, the subtract section 55 subtracts a signal obtained by multiplying the motor noise spectrum Sc stored in advance in the motor noise spectrum storage section 54 as a noise spectrum by a predetermined subtract coefficient α from the input sound spectrum Sb.
The spectrum changeover section 56 carries out changeover between the input sound spectrum Sb obtained from the Fourier transform section 53 and a sound spectrum Sd after the noise removal obtained from the subtract section 55 in response to a selection signal outputted from the control section 32 to supply the input sound spectrum Sb or the sound spectrum Sd to an inverse Fourier transform section 57. In particular, the spectrum changeover section 56 supplies, upon driving of the motor 21 such as during a zooming operation, the sound spectrum Sd after the noise removal to the inverse Fourier transform section 57 but supplies, in any other case, the input sound spectrum Sb to the inverse Fourier transform section 57.
The inverse Fourier transform section 57 inverse Fourier transforms the input sound spectrum Sb or the sound spectrum Sd after the noise removal inputted thereto through the spectrum changeover section 56 to obtain an original sound signal Se for each frame unit. A waveform synthesis section 58 synthesizes the sound signals Se for the individual frame units obtained by the inverse Fourier transform section 57 to restore a sound signal Sf which is continuous in a time series. The sound signal Sf is used as a final sound signal for recording and is recorded into a recording medium such as a memory together with video data obtained from the imaging system.